Hundreds of thousands of people were forced to evacuate from around the volcano on Java then when it roared to life late that year.
Officials say blasts during October and early November killed at least 44 people.
Japanese researchers say lava has re-entered Merapi’s crater, which is expanding and becoming more prone to explosive eruptions.
“... after its 2010 eruption, Merapi inflated again very quickly. This means that Merapi is a very active volcano,” said Kyoto University researcher Masako Iguchi.
He points out that before the 2010 blasts, Merapi had erupted in 2001 and 2006, recharging quickly between eruptive events.